1. Field of the Invention
This invention relates to an engine reversing detection system for an outboard motor, more particularly to a system for detecting reverse rotation of an internal combustion engine for an outboard motor for small boats.
2. Description of the Related Art
Small motor-driven boats are generally equipped with a propulsion unit including an internal combustion engine, propeller shaft and propeller integrated into what is called an outboard motor or engine. The outboard motor is mounted on the outside of the boat and the output of the engine is transmitted to the propeller through a clutch and the propeller shaft. The boat can be propelled forward or backward by moving the clutch from Neutral to Forward or Reverse position.
Specifically, the clutch is usually composed of a drive gear that rotates unitarily with the engine drive shaft when the engine is running, a forward gear, a reverse gear, and a dog (sliding clutch) located between the forward and reverse gears that rotates unitarily with the propeller shaft. The forward and reverse gears are engaged with the drive gear and rotate idly in opposite directions on the propeller shaft.
Since the outboard engine is connected to the propeller through the clutch of a relatively simple mechanism, when the engine speed is low and the engine output is small, for example, at the time of stopping the boat, the engine may sometimes driven by the propeller to rotate reverse. Here, xe2x80x9crotate reversexe2x80x9d indicates that the engine crankshaft rotates in a direction opposite to the predetermined direction such that the exhaust pipe in water functions as the intake pipe. If this happens, the exhaust pipe sucks sea (lake) water which may disadvantageously enter the cylinders, etc. The reverse rotation of the engine should preferably be detected.
In order to solve the problem, Japanese Laid-Open Patent Application No. Sho 62 (1987)-182463 teaches detecting the reverse rotation of a two-cycle, two-cylinder engine, using two sensors comprising a first sensor which generates a reference signal (TDC signal) at BTDC10 degrees of each cylinder and a second sensor which generates a unit crank angle signal at 15 degrees (in crank angle) obtained by dividing the interval of the reference signals by 12, and a counter which counts the number of the crank angle signals until it is reset by the reference signal. In the technique, the reverse rotation is detected when the counted value is not 12 and if the reverse rotation is detected, the engine is stopped.
Since, however, the prior art relates to the detection of reverse rotation in a two-cycle engine having only two cylinders, this technique can not immediately be applied to a four-cycle engine having three more cylinders, e.g., a six-cylinder engine.
An object of the present invention is therefore to solve the problem by providing an engine reversing detection system for an outboard motor, which can accurately detect reverse rotation of a four-cycle engine having three or more cylinders.
For realizing this object, there is provided a system for detecting reverse rotation of a 4-cycle internal combustion engine having three or more cylinders for an outboard motor mounted on a boat, whose output is connected to a propeller such that the boat is propelled forward or reverse, comprising: cylinder identifying means for identifying the cylinders of the engine; crank angle pulse generating means for generating a predetermined number of crank angle signals in a predetermined range of crank angles; counting means for counting the number of the crank angle singles; multiple count determining means for determining whether the counted value is a multiple of the predetermined number, when the cylinders are identified; and engine reversing determining means for determining that engine rotates reverse when the counted value is determined to be not the multiple of the predetermined number and for stopping the engine.